Common Acquired Melanocytic Nevi

Common nevi typically begin to develop in early childhood, and new nevi may continue to arise into the third decade (Figure 126-1). These lesions have a variety of presentations depending on where the nests of nevus cells reside, and they are named accordingly. Those with nevus cells at the dermal-epidermal junction are known as junctional nevi, and those with nevus cells in the dermis are intradermal nevi. Those with cells in both compartments are called compound. The shapes and sizes vary, but most are smaller than 6 mm in size. They are more common in sun-exposed areas, where increased sun exposure leads to more moles in these areas. In general, children with lighter pigmented skin have more nevi than those with darkly pigmented skin. Children with families with increased nevi also have more moles, suggesting a genetic component to the total number of lifetime moles acquired. Studies in first-degree relatives and twins suggest that genetic factors have a significant impact on the number of moles independent of skin color or sun exposure.

Figure 126-1 Common nevus.

The distribution of nevi can vary with skin pigmentation. Those with darker pigment have more nevi on acral locations, including the palms, soles, and nail beds. Nevi in acral sites are usually dark in color and have streaks of pigment that follow the dermatoglyphs.

Dysplastic or Atypical Nevi

These are atypical nevi that have some asymmetry, size larger than 6 mm, variable color, and irregular borders (Figure 126-2). They frequently contain both a macular and papular component and variegated color (pink, brown, tan). They show architectural disorder histologically and are categorized by many pathologists as mildly, moderately, or severely atypical. Atypical moles typically begin to develop around puberty. The tendency to develop these nevi is genetic, with some families having multiple atypical nevi but no family history of melanoma but other families having both an increased risk of atypical moles and melanoma (familial atypical mole and melanoma syndrome [FAMM]).

Figure 126-2 Dysplastic nevus.

Nevi that change in size, shape, color, or surface (bleeding, crusting, ulceration, thickening) or show signs of inflammation deserve evaluation and consideration for biopsy. Additionally, pain, itch, or tenderness also suggest that the nevus should be evaluated. With this said, however, symmetrical enlargement can be a normal finding in younger patients because the nevus grows with the patient. Uniform darkening after sun exposure can also occur. Chronic rubbing can also make nevi change color. Acquired nevi should be excised if they show signs of malignant transformation. They can also be removed surgically if they are in a location that is not practical for observation or if they are persistently irritated because of location such as at the waistline or neckline. All other nevi can be serially followed for change by skin examination, photography, or both.

When children have multiple moles, it is helpful to look at the clinical appearance of all of the nevi. Nevi are often very similar. This has been called the “signature” of the nevi and again highlights that nevi are programmed by genetics. A nevus that looks different from this signature should be looked at with suspicion. A new nevus is usually not concerning in a child or adolescent if it fits the signature. It is critical to perform a complete skin examination, including the scalp. Some evidence suggests that children who develop scalp nevi are at increased risk for acquiring a large number of nevi. Prophylactic removal of all nevi is not recommended because many melanomas develop de novo not from a preexisting nevus, and there is no evidence that removing all nevi decreases the risk of melanoma.

Congenital Nevi

Congenital melanocytic nevi (CMN) are characterized by being present at birth or within a few months of birth. Rarely, they do not become visible until up to 2 years of age. Congenital nevi are divided into giant (>20 cm), medium (1.5-2 0cm), and small (<1.5 cm). The colors of CMNs are variable with a range from tan to black. CMNs change over time. At birth and during early infancy, they may appear more uniform in color and flat. With time, they can become elevated and developed variegated pigmentation and a rough surface. Nodules and papules can develop within the lesion, and although most of these are benign, they need to be evaluated for malignant transformation. Over time, they can also develop dark terminal hairs (Figure 126-3).

Figure 126-3 Medium-sized congenital nevus.

Giant congenital nevi show the highest risk for neurocutaneous melanosis (melanocytes in the central nervous system [CNS]) and melanoma. The lifetime risk of melanoma in giant congenital nevi is 5% to 10%, but the peak risk is before puberty. This is in contrast to smaller congenital nevi, in which the risk for developing melanoma is highest after puberty. Neurocutaneous melanoma (NCM) occurs more commonly in patients with posterior axial giant congenital nevi and more than 20 satellite lesions. NCM is best detected by magnetic resonance imaging (MRI). There is some debate about screening MRIs to look for NCM because most patients with NCM are asymptomatic. If screening MRI is to occur, there is some evidence to suggest it should occur before the brain has myelinized (age 4 to 6 months). It is thought that myelin protein can obscure subtle deposits of melanocytes. Patients with lumbosacral lesions should have MRI to look for tethered cord or other abnormalities of the spine. NCM has been divided into symptomatic and asymptomatic forms. The prognosis for symptomatic NCM is poor even when patients do not develop melanoma. Neurologic manifestations typically occur before the age of 2 years but can present into the second and third decades of life. The clinical signs of NCM are most often related to the space-occupying effects of growing melanocytes in the CNS. These include but are not limited to headaches, vomiting, generalized seizures, cranial nerve palsies, and developmental delay. Structural CNS anomalies such as Dandy-Walker malformations have also been reported in patients with symptomatic NCM. NCM without symptoms is more common. It is still unclear whether these patients are at an increased lifetime risk of CNS melanoma or future neurologic symptoms.

Management of giant CMNs is difficult. Surgical excision (typically in stages and sometimes only partial) does decrease the incidence of melanoma. Prophylactic excisions should occur between 6 and 9 months of age because the risk of melanoma is high in infancy, but the anesthesia risk is lower after 6 months of age. However, it should be noted that even total resection does not eliminate the risk of melanoma because it is impossible to excise all nevus cells because these nevus cells often track deep, and there may be other sites in CNS. Additionally, many giant CMNs are not operable. There must always be a risk : benefit analysis before surgery. The low incidence of melanoma overall may be a reason to follow patients clinically rather than perform large surgeries that can have cosmetic and long-term consequences (including other cancers such as squamous cell carcinoma occurring in the scar). Treatment decisions are tailored for each patient. All CMN patients and their parents need proper instruction in self-skin examinations, which should be performed each month. They need education about atypical changes they should be looking for in the lesions, including changes in size, shape, or color as well as development of papules, nodules, bleeding, or ulceration. Cutaneous photography can be helpful to follow lesions. Physical examinations should be scheduled regularly with total skin exams, including palpation of the nevus and any scars, examination of lymph nodes, and a complete review of systems. Biopsy of suspicious lesions should not be delayed.

The management of small and medium melanocytic nevi is controversial. The lifetime risk of developing melanoma is somewhere between 0% and 5%, and it is rare to undergo malignant transformation in childhood. Lesions can be followed and surgically removed in later childhood when the child can participate in the decision. The risk for melanoma increases in puberty. If it is decided not to remove the lesion, serial examinations and photographs should be used for evaluation. Surgery should be considered sooner if it is burdensome to follow the lesion for the patient and family or anxiety is high. If a change is noted, the lesion should be biopsied. Patients and their families should be aware of CMN support groups such as Nevus Network (www.nevusnetwork.org).

Special Nevi

Blue Nevus

These are blue papules or nodules that typically begin in adolescence and grow slowly (Figure 126-4). They are composed of dermal melanocytes and melanophages, and the depth of the melanocytes in the dermis accounts for their blue color. There are three variants: common, cellular, and epitheloid. The common type is usually solitary on the dorsal hands and feet and occasionally the face. The cellular type has a predilection for the buttock and sacral region and occasionally is present at birth. Epithelioid blue nevi can be numerous and can be seen in Carney’s complex (a disorder of myxomas, lentigines, endocrine abnormalities or neoplasms, and schwannomas). Melanomas can rarely arise in blue nevi. Clinically, the dark blue color may resemble a nodular melanoma. Usually, the clinical history of slow growth is what distinguishes the two. Small blue nevi can be followed clinically. Those in difficult locations to follow such as the scalp or sacrococcygeal area can be surgically removed.

Figure 126-4 Blue nevus.

Halo Nevi

These are lesions that are characterized by a central pigmented nevus surrounded by an area of depigmentation (Figure 126-5). These occur most commonly in adolescents on the back. They occur in 5% of white children 6 to 15 years of age. The central area may darken but more commonly lightens or regresses over time. There are many lymphocytes surrounding the melanocytes on histology, suggesting an immunologic response to the nevus cells. Halo nevi may herald the onset of vitiligo. Regressing melanoma may also have an associated leukoderma, but typically it is not a symmetrical process as in the halo nevus. Full examination is indicated to rule out a concurrent melanoma. The decision to biopsy the central nevus is based on the same criteria as for other acquired nevi.

Figure 126-5 Halo nevus.